Due to the frequency of injury to the anterior cruciate ligament (ACL), especially in sports, and similar injury to other ligaments and related structures, there is a great deal of prior art dealing with replacement of these structures with graft ligaments. Much of this prior art is concerned principally with ensuring proper alignment of bone tunnels drilled in the tibia and femur to receive the opposed ends of the graft ligament, with proper preparation of the surgical site, i.e., by removing sufficient bone to allow the graft to function properly, and with preparation of suitable graft ligaments, commonly by harvesting donor bone/tendon/bone structures from the knee of the patient. See generally, "The Paramax ACL Guide System Surgical Technique", a brochure published by Linvatec Corporation of Largo, Florida in 1992, and incorporated by reference herein, which provides useful background on one type of overall ACL replacement procedure. Other sources of replacement ligaments, including allograft and autograft ligament substitutes, are within the skill of the art and are intended to be included within "graft ligament" as used herein.
The present invention does not address these aspects of ACL reconstruction, but instead addresses the problem of securely anchoring the graft ligament in the bone tunnels. More specifically, the present invention relates to improvements in devices to be disposed at the outer ends of bone tunnels to provide a fixing point for sutures securing an end of a graft ligament in place.
The prior art shows numerous devices for anchoring sutures for holding graft ligaments in place. For example, Zang U.S. Pat. No. 5,522,843 and Greenfield U.S. Pat. No. 5,584,835 show anchors adapted to be threaded into bores in bone and having apertures for receiving sutures. However, these structures are intended for use where the graft ligament is intended to lie substantially along the surface of a bone; the present invention is concerned with devices to be used at the end of bone tunnels and securing a suture extending inwardly through the bone tunnel.
Other patents show anchors for ligaments and similar structures wherein the structure to be fixed is sutured to an anchor threaded into a bone tunnel; see, for example, U.S. Pat. No. 5,156,616 to Meadows et al and U.S. Pat. No. 5,152,790 to Rosenberg et al. The art also suggests retaining a graft ligament in a bone tunnel by confining the ligament between a conical plug and the bone tunnel, so that the ligament is held in place by friction. See U.S. Pat. No. 4,744,793 to Parr et al and U.S. Pat. No. 4,708,132 to Silvestrini. It would be preferred to avoid the complexity of these types of anchor where possible.
Martins et al U.S. Pat. No. 5,306,290 shows a "Suture Button" comprising a frusto-conical member defining a recess for receiving a knot. This device could be placed in a bone tunnel and sutures from a graft ligament drawn through apertures in a planar surface forming the bottom of the recess; after suitably tensioning the ligament by tension applied to the suture, the knot can be tied, securing the ligament. However, this device would appear to be susceptible to being drawn into the bone tunnel by excessive tension.
Additional references show anchors for ligaments wherein the ligament is sutured to an anchor configured to abut the outer opening of the bone tunnel, and remain outside the bone tunnel. See for example Graf et al U.S. Pat. No. 5,306,301, disclosing various "elongated bodies" intended to be passed through the bone tunnels and rotated after exiting the tunnels, so as to be retained against the outer surface of the bone. See also U.S. Pat. No. 5,139,520 to Rosenberg, especially at column 11, lines 39-62.
German pat. no. DE 196 16 122 C1 to Eichborn et al is of the same general class and discloses several embodiments of anchor or "button" structures for securing ligaments in place. In one embodiment, the Eichborn anchor is of generally hat-shape configuration, comprising a round flange surrounding the rim of a hemispheric dome-shaped body having a depressed center section, forming a recess. The center section is sized to be received in the opening of a bone tunnel, and has apertures extending therethrough for receiving sutures, while the outermost flange portion of the Eichborn anchor abuts the outer surface of the bone, preventing the anchor from being pulled into the bone tunnel. The Eichborn anchor may be elliptical in outline, to conform to tunnels formed at an angle to the surface of the bone; see FIGS. 3 and 4. Accordingly, sutures can be passed through the apertures and tensioned and tied as discussed in connection with the Martins patent, to secure a graft ligament; the depressed recess receives the suture knot. The Eichborn anchor is of uniform thickness across the flange and dome, limiting its strength, and the placement of the suture-receiving apertures is not optimal for use in ligament reconstruction.
Other U.S. patents generally relevant to the subject matter of this application include U.S. Pat.No. 4,708,132 to Silvestrini; U.S. Pat. No. 4,744,793 to Parr et al; U.S. Pat. No. 5,571,139 to Jenkins, Jr.; U.S. Pat. No. 4,997,433 to Goble et al; U.S. Pat. No. 5,562,671, also to Goble et al; U.S. Pat. No. 5,261,914 to Warren; and U.S. Pat. No. 5,380,334 to Torrie et al.